1. Field
The present invention relates generally to fluid dynamic bearings (FDB), and more particularly to FDB's as used in motors for disc drive storage systems.
2. Related Art
Magnetic disc drives are used for magnetically storing information. In a magnetic disc drive, a magnetic disc rotates at high speed and a transducing head “flies” over a surface of the disc. This transducing head records information on the disc surface by impressing a magnetic field on the disc. Information is read back using the head by detecting magnetization of the disc surface. The transducing head is moved radially across the surface of the disc so that different data tracks can be read back.
Over the years, storage density has tended to increase and the size of the storage system has tended to decrease. This trend has led to greater precision and lower tolerance in the manufacturing and operating of magnetic storage discs. For example, to achieve increased storage densities the transducer head is placed increasingly close to the surface of the storage disc to track increasingly densely positioned data tracks. As the density of the data tracks increases it is generally desired that the disc rotate substantially in a single plane with reduced run-out. A slight wobble or non-repeatable run-out in disc rotation can limit track spacing to account for misreads by the transducer head, thereby lowering track density. Accordingly, it is desired to reduce and minimize non-repeatable run-out in the system.
From the foregoing discussion, it can be seen that the stability of the bearing assembly supporting the storage disc is of importance. One typical bearing assembly comprises ball bearings supported between a pair of races, which allow a hub of a storage disc to rotate relative to a fixed member.
An alternative bearing design is a fluid dynamic bearing. A fluid dynamic bearing provides a lubricating fluid such as gas or a liquid in a bearing gap between a fixed member and a rotating member.
Gas dynamic bearings have been recognized as being suitable for lower power applications because the viscosity of gas is lower than conventional lubricating liquids, such as oil. Gas dynamic bearings typically have less damping than a fluid bearing and tend to provide wear properties inferior to liquid bearings at low rotational speeds, such as those during spin-up of discs in a drive. Liquid dynamic bearings generally have better damping characteristics and tend to provide relatively high lubricity during spin-up.